Extrusion Coating Polyethylene

ABSTRACT

The present invention relates to a polymer composition with good chemical properties and barrier properties being multimodal and comprising a polymer (A) having a weight average molecular weight of lower than 6000 g/mol and a polyolefine (B) having a higher weight average molecular weight than polymer (A) and a filler (C), whereby a polymer composition without filter (C) has a density of 940 kg/m 3  or lower.

The present invention relates to a polymer composition suitable forextrusion coating and films, preferably cast films having good chemicalproperties and barrier properties, in particular, a low water-vaportransmission rate (WVTR) and a low curling. Additionally, the presentinvention relates to the process for producing the inventive compositionand its use. Moreover, the present invention is related to a multi-layermaterial comprising the polymer composition as well as to a process ofsaid multi-layer material.

One of the largest and most rapidly growing polyolefin-processing methodis extrusion coating. The largest single volume of coated materials aredifferent papers and paperboards, which are used for a variety ofpackaging applications. Other material frequently coated are polymerfilms, cellophane, aluminium foil, freezer wrap paper and fabrics ofvarious kinds. One target for the improvement of coated articles is toreduce the water-vapor transmission rate (WVTR) as much as possible. Acoated material with a low water-vapor transmission rate (WVTR) can forexample protect the products wrapped therein much better. The demandedrequirement applies, of course, not only to coated materials but also tocast films used for packaging or containers. In both cases, a lowwater-vapor transmission rate is required. Much effort has beenundertaken to improve the water-vapor transmission rate of coatedmaterials as well as for cast films. To date, several new polymercompositions have been developed and much effort has been undertaken tofind appropriate fillers to improve the barrier propertiessignificantly. Furthermore, different polymers have been designed ascyclo-olefin copolymers (COC) and liquid crystal polymers (LCP).However, these materials have the drawback of being expansive and havingminor processability properties.

WO 00/71615 discloses for example the use of a bimodal high densitypolyethylene (HDPE) with a melt flow rate, MFR₂, of 5 g/10 min and adensity of 957 kg/m³ for extrusion coating. No information is given howto improve the water-vapor transmission rate (WVTR).

WO 00/34580 describes release liner for pressure-sensitive adhesivelabels. The release-liner contains a paper wrap, a filled polymer layer,and, on the opposite of the paper web, an extrudate, e.g. polyethylene,and on the top of the extrudate, a release film. The filled polymerlayer can be polyethylene and the filler is an inert particulate, suchas silica, mica, clay, talc and titanium oxide. The filler is present in15 to 40 wt % of the composition.

U.S. Pat. No. 4,978,572 describes a laminated film having three layers.The first layer comprises a thermoplastic resin and 0.3 to 30 wt % whiteinorganic particles. The second one comprises an ethylene copolymer, 0.5to 90 wt % of a substance giving anti-block action and anti-oxidant. Thethird one comprises a metallized thermoplastic. The substance givinganti-block action of the second layer may be silica or talc. Thelaminated film is reported to have good mechanical strength and goodbarrier properties.

Even though the prior art offers already a variety of products havinggood water-vapor transmission rates (WVTR), there is still demand for asignificant improvement of these properties. One significantdisadvantage in polymer compositions comprising fillers reducing thewater-vapor transmission rate (WVTR) is the low dispersion of thefillers incorporated in the polymer matrix. Conventional mechanicalincorporation frequently results in poor dispersion as usual fillersform multi-layer aggregation caused by incompatibility with polymermatrix. One consequence of the described phenomenon is that thewater-vapor transmission rate (WVTR) varies considerably in the layerleading to unsatisfying average values for the WVTR. Secondly, the lowdispersion of the filler causes an easy upcurling of the polymercomposition coated on the materials. Hence, a uniform dispersion offillers incorporated in a polymer composition should improve thewater-vapor transmission rate significantly, and, additionally, thecurling properties of a coated material should be enhanced.

Hence, the object of the present invention is to improve the water-vaportransmission rate (WVTR).

The present invention is based on the finding that the object can beaddressed by a polymer composition comprising a polymer having a lowaverage molecular weight enabling an enhanced and uniform dispersion offillers incorporated in the polymer composition.

The present invention therefore provides a multimodal polymercomposition comprising

-   a) at least one polymer (A) having a weight average molecular weight    (M_(w)) of lower than 60,000 g/mol;-   b) at least one polyolefin (B) having a higher weight average    molecular weight (M_(w)) than polymer (A); and-   c) a filler (C) whereby    -   the polymer composition without filler (C) has a density of 940        kg/m³ or lower.

It is preferred that the polymer composition consists of

-   a) at least one polymer (A) having a weight average molecular weight    (M_(w)) of lower than 60,000 g/mol;-   b) at least one polyolefin (B) having a higher weight average    molecular weight (M_(w)) than polymer (A); and-   c) a filler (C) whereby    -   the polymer composition without filler (C) has a density of 940        kg/m³ or lower.

Accordingly the polymer composition according to this invention ismultimodal with respect to the molecular weight distribution.“Multi-modal” or “multimodal distribution” describes a frequencydistribution that has several relative maxima. In particular, theexpression “modality of a polymer” refers to the form of its molecularweight distribution (MWD) curve, i.e. the appearance of the graph of thepolymer weight fraction as a function of its molecular weight. Themolecular weight distribution (MWD) of a polymer produced in a singlepolymerization stage using a single monomer mixture, a singlepolymerization catalyst and a single set of process conditions (i.e.temperature, pressure, etc.) shows a single maximum the breadth of whichdepends on catalyst choice, reactor choice, process conditions, etc.,i.e. such a polymer is monomodal.

This inventive composition is characterized by a very low water-vaportransmission rate (WVTR) and also by low curling-values forextrusion-coated layers. These improved properties are reached by a muchbetter dispersion of the filler (C) in the polymer mixture of polymer(A) and polyolefin (B) compared with an unmimodal polymer having thesame melt index and density for both extrusion-coated layers and castfilms.

Hence, the polymer composition according to this invention is amultimodal including bimodal polymer composition consisting of at leasttwo different polymers having two different molecular weightdistribution curves and are blended mechanically or in situ during thepreparation thereof. Preferably the polymer composition is at least abimodal mechanical or in-situ blend of a polyolefin (1) (as polymer (A))and polymer (B). In case such a bimodal blend comprises further a wax(2) as an additional polymer (A), then the final polymer composition mayalso be trimodal.

The molecular weight distribution (MWD) is the relation between thenumbers or molecules in a polymer and their individual chain length. Themolecular weight distribution (MWD) is often given as a number, whichnormally means weight average molecular weight (M_(w)) divided by numberaverage molecular weight (M_(n)).

The weight average molecular weight (M_(w)) is the first moment of aplot of the weight of polymers in each molecular weight range againstmolecular weight. In turn, the number average molecular weight (M_(n))is an average molecular weight of a polymer expressed as the firstmoment of a plot of the number of molecules in each molecular weightrange against the molecular weight. In effect, this is the totalmolecular weight of all molecules divided by the number of molecules.

The number average molecular weight (M_(n)) and the weight averagemolecular weight (M_(w)) as well as the molecular weight distribution(MWD) are determined according to ISO 16014.

The weight average molecular weight (M_(w)) is a parameter for thelength of the molecules in average. Low M_(w)-values indicate that thechain length of the molecules is rather short in average. It has beenfound out that a polymer mixture comprising a polymer (A) withM_(w)-values of lower than 60,000 g/mol contributes inter alia to betterbarrier properties and better dispersion of the filler (C). Such betterdispersion improves the water-vapor transmission rate (WVTR) as well asthe curling resistance positively.

Hence, as a further requirement of the present invention, the multimodalpolymer composition must comprise at least one polymer (A) having aweight average molecular weight (M_(w)) of lower than 60,000 g/mol. Itis in particular preferred that at least one polymer (A) having a weightaverage molecular weight (M_(w)) of lower than 60,000 g/mol is at leastone polyolefin (1) having a weight average molecular weight (M_(w)) of10,000 to 60,000 g/mol, more preferably of 20,000 to 50,000 g/mol and/orat least one wax (2) having a weight average molecular weight (M_(w)) ofless than 10,000 g/mol, more preferably in the range of 500 to 10,000g/mol.

Moreover, it is preferred that the polyolefin (1) is a polyethylene orpolypropylene, more preferably a polyethylene. The polyolefin (1) can bea homopolymer or copolymer. It is preferred that the polyolefin (1) is ahomopolymer or copolymer of propylene or ethylene, more preferred thepolyolefin (1) is a homopolymer or copolymer of ethylene. Mostpreferably the polyolefin (1) is a low density polyethylene (LDPE), alinear low density polyethylene (LLDPE), or a linear medium densitypolyethylene (LMDPE). LDPE, LLDPE and LMDPE are equally suitablealternatives for polyolefin (1), e.g. where a LLDPE or a LMDPE isapplicable also a LDPE can used and vice versa.

In case polymer (A) is a wax (2), it is preferred that it is selectedfrom one or more of

-   (2a) a polypropylene wax having a weight average molecular weight    (M_(w)) of less than 10,000 g/mol, more preferably in the range of    500 to 10,000 g/mol, still more preferably in the range of 1000 to    9000 g/mol, yet more preferably in the range of 2000 to 8000 g/mol    and most preferably in the range of 4000 to 8000 g/mol or a    polyethylene wax having a weight average molecular weight (M_(w)) of    less than 10,000 g/mol, more preferably in the range of 500 to    10,000 g/mol, still more preferably in the range of 1000 to 9000    g/mol, yet more preferably in the range of 2000 to 8000 g/mol and    most preferably in the range of 4000 to 8000 g/mol, and-   (2b) an alkyl ketene dimer wax having weight average molecular    weight (M_(w)) of less than 10,000 g/mol, more preferably lower than    5000 g/mol, yet more preferably lower than 1000 g/mol. In turn the    alkyl ketene dimer wax has preferably weight average molecular    weight (M_(w)) of at least 100 g/mol. Most preferred the alkyl    ketene dimer wax has weight average molecular weight (M_(w)) in the    range of 250 to 1000 g/mol.

The terms “at least one polymer (A)”, “at least one polyolefin (1)” or“at least one wax (2)” shall indicate that more than one polymer (A),polyolefin (1) or wax (2) can be present in the multimodal polymercomposition. It is preferred that three, two or one different polymers(A) as defined above are used in a multimodal polymer composition. Stillmore preferred is that wax (2), preferably a polypropylene wax (2a) oran alkyl ketene dimer wax (2b) as defined above is used as a component(A) only. In case the component (A) comprises a polyolefin (1) asdefined above, it is preferred that a wax (2) is present in themultimodal polymer composition as a further polymer (A). In such casesthe multimodal composition is preferably trimodal comprising polyolefin(1), wax (2) and polyolefin (B) having different centered maxima intheir molecular weight distribution, e.g. having different weightaverage molecular weights (M_(w)). The use of the wax (2) has thebenefit that the amorphous region of the polymer matrix, which may be amix of polyolefin (1) and polyolefin (B), is filled up and improvesthereby the barrier properties.

It is preferred that not only the final polymer composition has aspecific density of 940 kg/m³ or lower but also the polymer (A) shallhave a density of lower than 945 kg/m³. It is preferred that polyolefin(1) when used as polymer (A) has a density lower than 945 kg/m³, morepreferably is in a range of 905 to 935 kg/m³, still more preferably inthe range of 910 to 930 kg/m³ and most preferred in the range of 915 to925 kg/m³. Preferably, the polyolefin (1) is a linear low densitypolyethylene (LLDPE) or a linear medium density polyethylene (LMDPE). Inturn, also a low density polyethylene (LDPE) produced in a high pressureprocess by free radical polymerization is applicable as a polyolefin(1). The linear low density polyethylene (LLDPE) or the linear mediumdensity polyethylene (LMDPE) is produced by a process as described forthe polyolefin (B) below.

The molecular weight distribution (MWD) of the polymer composition isfurther characterized by the way of its melt flow rate (MFR) accordingto ISO 1133 at 190° C. The melt flow rate (MFR) mainly depends on theaverage molecular weight. The reason for this is that long moleculesgive the material a lower flow tendency than short molecules.

An increase in molecular weight means a decrease in the MFR-value. Themelt flow rate (MFR) is measured in g/10 min of the polymer dischargedunder specific temperature and pressure conditions and is the measure ofa viscosity of the polymer which in turn for each type of polymer ismainly influenced by its molecular weight distribution, but also by itsdegree of branching. The melt flow rate measured under a load of 2.16 kg(ISO 1133) is denoted as MFR₂. In turn, the melt flow rate measured with5 kg load (ISO 1133) is denoted as MFR₅.

In case polymer (A) is a polyolefin (1), it is preferred that MFR₂ is inthe range of 1.0 to 20.0 g/10 min and more preferably in the range of2.0 to 15.0 g/10 min and for example in the range of 3.0 to 10.0 g/10min. According to one embodiment, the polyolefin (1) is a linear lowdensity polyethylene (LLDPE) or a linear medium density polyethylene(LMDPE) with MFR₂ as given above. In turn, polyolefin (1) can also be alow density polyethylene (LDPE) having a density in the range as statedin this paragraph. The low density polyethylene (LDPE) is produced in ahigh-pressure process by free radical polymerization. In turn, thelinear low density polyethylene (LLDPE) or the linear medium densitypolyethylene (LMDPE) is produced as described for polyolefin (B).

In case polymer (A) is an ethylene homopolymer, it is preferred that theethylene homopolymer contains less than 0.2 mol %, more preferably lessthan 0.1 mol % and most preferably less than 0.05 mol % units derivedfrom alpha-olefins other than ethylene. It is in particular preferredthat the polymer (A) is an ethylene copolymer, more preferably having aweight average molecular weight from 10,000 to 60,000 g/mol, still morepreferably from 20,000 to 50,000 g/mol. Yet more preferably the polymer(A) is an ethylene copolymer having a density of 905 to 935 kg/m³, morepreferably of 910 to 930 kg/m³, most preferably of 915 to 925 kg/m³ andhaving a melt index MFR₂ from 1.0 to 20.0 g/10 min, more preferably from2.0 to 15.0 g/10 min, most preferably of 3.0 to 10.0 g/10 min.Preferably, the ethylene copolymer comprises, more preferably consistsof, comonomer units as defined below for the LLDPE. It is in particularpreferred that the ethylene copolymer fulfills all properties as statedabove simultaneously.

In case polymer (A) is a wax (2a), namely a polypropylene wax or apolyethylene wax, it is preferred that the wax (2a) has a weight averagemolecular weight (M_(w)) in the range of 500 to 10,000 g/mol, morepreferably in the range of 1,000 to 9,000 g/mol, still more preferablyin the range of 2,000 to 8,000 g/mol and most preferably in the range of4,000 to 8,000 g/mol. Further preferred ranges for the weight averagemolecular weight (M_(w)) of the wax (2a), in particular thepolypropylene or polyethylene wax, is in the range of 4,000 to 7,000g/mol, still more preferably in the range of 5,000 to 6,000 g/mol andmost preferably in the range of 5,300 to 5,400 g/mol. Additionally, itis preferred that the wax (2a), in particular the polypropylene wax orpolyethylene wax, has a z-average molecular weight of 9,100 to 40,000g/mol, more preferably from 500 to 20,000 g/mol and most preferably from10,000 to 12,000 g/mol. It is additionally preferred that the wax (2a),in particular the polypropylene wax or the polyethylene wax, has anumber average molecular weight (M_(n)) of 100 to 20,000 g/mol, morepreferably of 500 to 3,000 g/mol.

Moreover, it is preferred that wax (2a), in particular polypropylene waxor polyethylene wax, has a specific molecular weight distribution (MWD)which is the relation between the number of molecules in the polymer andtheir individual chain length. The molecular weight distribution isgiven as a number which means weight average molecular weight divided bynumber average molecular weight (M_(w)/M_(n)). It is preferred that thewax (2a), in particular the polypropylene wax or the polyethylene wax,has an MWD in the range of 1 to 5, more preferably in the range of 1.5to 4.

In addition, it is preferred that the wax (2a), in particular thepolypropylene wax or the polyethylene wax, has a melting temperature inDSC-analysis of below 150° C., more preferably below 140° C., still morepreferably in the range of 95 to 130° C., most preferably in a range of105 to 115° C.

In case a wax (2b), namely an alkyl-ketene dimer, is employed as polymer(A), it is preferred that the weight average molecular weight (M_(w)) ofthe wax (2b) is higher than 100 g/mol. In turn, it is preferred that theweight average molecular weight of the wax (2b) is lower than 10,000g/mol, more preferably lower than 5,000 g/mol, still more preferablylower than 1,000 g/mol. Preferred ranges for the weight averagemolecular weight (M_(w)) of the wax (2b) is 100 to 10,000 g/mol, morepreferably 250 to 1,000 g/mol. Additionally, it is preferred that thewax (2b) has a number average molecular weight (M_(n)) of 100 to 20,000g/mol, more preferably in the range of 100 to 800 g/mol. In addition, itis preferred that wax (2b) has a melting temperature in DSC-analysisbelow 140° C., more preferably below 100° C. A preferred range for themelting temperature in DSC-analysis is 50 to 90° C., more preferably 50to 70° C.

As a further requirement, according to the present invention, thepolyolefin (B) shall have a higher weight average molecular weight(M_(w)) than polymer (A). It is preferred that the polyolefin (B) has aweight average molecular weight (M_(w)) of higher than 80,000 g/mol,more preferably higher than 100,000 g/mol. The upper limit for theweight average molecular weight for polyolefin (B) shall preferably notbe higher than 300,000 g/mol, more preferably not higher than 200,000g/mol. The preferred range for the weight average molecular weight forpolyolefin (B) is 80,000 to 300,000 g/mol, more preferably from 100,000to 200,000 g/mol. Preferably, polyolefin (B) is a linear low densitypolyethylene (LLDPE) or a linear medium density polyethylene (LMDPE),which has been preferably produced in a low medium pressure process inthe presence of a polymerization catalyst (i.e. a Ziegler-Natta catalystor a metallocene catalyst). A linear low density polyethylene (LLDPE)and a linear medium density polyethylene (LMDPE) has a density lowerthan 945 kg/m³, more preferably in the range of 905 to 935 kg/m³, stillmore preferably in the range of 910 to 930 kg/m³ and most preferred inthe range of 915 to 925 kg/m³. However, also a low density polyethylene(LDPE) is also applicable for the polyolefin (B). A low densitypolyethylene (LDPE) has the same density ranges as the LLDPE or theLMDPE as stated in this paragraph and is a product from a high pressurepolymerization process characterized by a highly branched chainstructure. LDPE, LLDPE and LMDPE are equally suitable alternatives forpolyolefin (B), e.g. where a LLDPE or a LMDPE is applicable also a LDPEcan used and vice versa.

According to this invention, more than one polyolefin (B) can be used.Accordingly, the invention also comprises the possibility of any mixtureof a linear low density polyethylene (LLDPE), a linear medium densitypolyethylene (LMDPE) and a low density polyethylene (LDPE).

The MFR₂ of the polyolefin (B) is preferably in the range of 1.0 to 20.0g/10 min, more preferably in the range of 2.0 to 15.0 g/10 min, in therange of e.g. 3.0 to 10.0 g/10 min. It is in particular preferred thatthe linear low density polyethylene (LLDPE) and the linear mediumdensity polyethylene (LMDPE) have such melt flow characteristics. Inturn, also the low density polyethylene (LDPE) suitable as a polyolefin(B) may have the melt flow characteristics as given in this paragraph.

It is preferred that the polyolefin (B) is a polyethylene. In case thepolyolefin (B) is a polyethylene, it may be an ethylene homopolymer oran ethylene copolymer. In case for the polyolefin (B) an ethylenehomopolymer is employed, then preferably an ethylene homopolymer is usedas defined for polymer (A). In case an ethylene copolymer is employedfor polyolefin (B), then preferably an ethylene copolymer is used asdefined below. It is in particular preferred that polyolefin (B) is alow density polyethylene (LDPE), a linear low density polyethylene(LLDPE) or a linear medium density polyethylene (LMDPE).

According to one embodiment, the polymer composition according to thisinvention is a linear low density polyethylene (LLDPE) comprisingpolyolefin (1) (polymer (A)) as a low molecular weight fraction of LLDPEand polyolefin (B) as a high molecular weight fraction of LLDPE. Thislinear low density polyethylene (LLDPE) may be a mechanical blend,preferably an in-situ blend produced in a multistage process. Preferablysaid composition comprises wax (2) as a further polymer (A).

It is preferred that the polymer composition as defined above comprises1 to 50 wt % of polymer (A), 40 to 90 wt % of polyolefin (B) and 1 to 50wt % of filler (C), more preferably of 5 to 40 wt %, and most preferablyof 10 to 35 wt %. In case the polymer composition is produced in an insitu polymerization process, e.g. a sequential step process by utilizingreactors coupled in series and described as above, it is preferred thatthe polymer (A) may range from 40 to 60 wt %, more preferably 49 to 55wt % in the polymer mix without filler (C). In turn, it is preferredthat in such a polymer mix, the polyolefin (B) ranges from 60 to 40 wt%, more preferably from 51 to 45 wt %. Preferably, the total polymercomposition comprises 50 to 99 wt % of said polymer mix and of 1 to 50wt % filler (C), more preferably of 5 to 40 wt %, and most preferably of10 to 35 wt %.

In case polymer (A) and polyolefin (B) are blended mechanically, it ispreferred that polymer (A) ranges from 1 to 30 wt % and, morepreferably, from 1 to 20 wt % in the total polymer composition. Theseranges apply in particular in case for polymer (A) a wax (2) is usedonly.

The last requirement according to the present invention is that themultimodal polymer composition additionally comprises a filler (C). Anyfiller having a positive influence on the water-vapor transmission rate(WVTR) can be used. Preferably, the filler shall be lamellar, such asclay, mica or talc. More preferably, the filler shall be finely divided.The finely divided filler consists of about 95 wt % of particles havingparticle sizes of less than 10 μm, and about 20-30 wt % of particleshaving a particle size of less than 1 μm. In the present invention alllayer materials may be used as long as they have the ability to dispersein the polymer composition. The filler may either be a clay-basedcompound or a submicron filler such as talc, calcium carbonate or mica,which usually have been treated, for instance by grinding, to obtainparticles of small, i.e. submicron, dimensions, in situ as stated above.

It is preferred that the filler (C) is layered silicate material, stillmore preferred, filler (C) is a clay-based compound. Clay-basedcompounds upon compounding of the polymer composition are dispersed inthe polymer composition so that individual platelets in the layeredstructure are separated.

In a further preferred embodiment, the filler (C) is a clay-basedlayered inorganic, preferably silicate material or material mixture.Such useful clay materials include natural, synthetic and modifiedphyllosilicates. Natural clays include smectite clays, such asmontmorillonite, hectorite, mica, vermiculate, bentonite. Syntheticclays include synthetic mica, synthetic saponite, synthetic hectorite.Modified clays include fluorinated montmorillonite, fluorinated mica.

Of course, the filler (C) may also contain components comprising amixture of different fillers, such as mixtures of a clay-based fillerand talc.

Layered silicates may be made organophylic before being dispersed in thepolymer composition by chemical modification, such as by cation-exchangetreatment using alkyl ammonium or phosphonium cation complexes. Suchcation complexes intercalate between the clay layers.

Preferably, a smectite type clay is used, which comprisesmontmorinollite, beidellite, nontronite, saponite, as well as hectonite.The most preferred semicite type clay is montmorinollite.

Preferably, also talc is used as a filler (C).

The density affects most physical properties like stiffness impactstrength and optical properties of the end products. Hence, andaccording to the present invention, the density of the polymercomposition shall be of 945 kg/m³ or lower. More preferably, the densityshall range from 905 to 935 kg/m³, still more preferably from 910 to 930kg/m³ and most preferably from 915 to 925 kg/m³.

The ranges and values given for the density in the whole invention applyfor pure polymer compositions and do not include any additives, inparticular no filler (C). The density is determined according to ISO1183-1987.

Moreover, it is preferred that the polymer composition without anyadditive, preferably without filler (C) has a melt flow rate MFR₂according to ISO 1133 at 190° C. of 5 to 20 g/10 min, more preferablyfrom 7 to 15 g/10 min.

Preferably, the polymer composition without any additive, preferablywithout filler (C) has a melt flow rate MFR₅ according to ISO 1133 at190° C. of 20 to 40 g/10 min, more preferably of 25 to 35 g/10 min.

Moreover, it is preferred that the melt flow ratio, which is a ratio oftwo melt flow rates measured for the same polymer under two differentloads, falls within a specific range. The preferred specific range is2.5 to 4.5, more preferably 2.7 to 4.0, for the melt flow ratioMFR₅/MFR₂.

A further characteristic of the molecular weight distribution (MWD)which is the relation between the number of molecules in a polymer andtheir individual chain length has to be considered. The width of thedistribution is a number as a result of the ratio of the weight averagemolecular weight divided by the number average molecular weight(M_(w)/M_(n)). In the present invention, it is preferred that thepolymer composition without any additive, preferably without filler (C),has a M_(w)/M_(n) of preferably 8 to 25 and more preferably from 10 to20.

Additional additives, e.g. inorganic additives, known as exipients andextrusion aids in the field of coatings and films, are used.

For a better adhesion between the coating and the substrate, it ispreferred that the polymer is oxidized. Consequently, it is preferredthat the polymer composition contains anti-oxidants and processstabilizers less than 2,000 ppm, more preferably less than 1,000 ppm andmost preferably not more than 700 ppm. The anti-oxidants thereby may beselected from those known in the art like those containing hinderedphenols, secondary aromatic amines, thio-ethers or othersulfur-containing compounds, phosphites and the like including theirmixtures.

It has been found that the polymer composition as described above has avery low water-vapor transmission rate (WVTR). Additionally, thecomposition has a good adhesion to the substrate, in particular toaluminium, without any need to have an adhesion layer between thesubstrate and the coating. Further, the tendency of the coated articleto curl is significantly reduced for the polymer composition compared toneat polymer. These advantageous effects could only be achieved as themiscibility between the polymer and the filler is much higher for amultimodal or bimodal polymer having a low molecular weight polymerfraction in comparison with a polymer having the same melt index anddensity.

In one preferable embodiment, the multimodal composition comprises aspolymer (A), which is the low molecular weight fraction, a polyolefin(1), more preferably a low density polyethylene (LDPE) or linear lowdensity polyethylene (LLDPE). The polyolefin (B), which is the highmolecular weight fraction, is a low density polyethylene (LDPE) or alinear low density polyethylene (LLDPE). Preferably, this compositioncomprises a further polymer (A) which is a wax (2) as defined above.This composition can be produced in an in situ process or can be blendedmechanically. Preferred properties for the polymer (A), in particularthe polyolefin (1), the wax (2) and the polyolefin (B) are those asgiven above. In case this composition comprises two polymers (A), namelya polyolefin (1) and a wax (2), it is preferred that the amount of wax(2) in the total composition without filler (C) is 1 to 30 wt %, morepreferably 1 to 20 wt % and most preferably 1 to 10 wt %. In turn, thecomposition comprises 70 to 99 wt %, more preferably 80 to 99 wt % andmost preferably 90 to 99 wt % of LLDPE resulting from polymer (A) andpolyolefin (B). In case the composition comprises LDPE, it is preferredthat wax (2) is present in the amount of 1 to 30 wt % and LDPE resultingat least from polymer (B) and optionally from polymer (A) and is presentin the amount of 70 to 99 wt % in the total composition without filler(C).

In another preferable embodiment, a polymer composition is produced inan in situ process, whereby the sequential step process by utilizingreactors coupled in series as described above is preferred. Preferablypolymer (A) is produced in a loop reactor whereas polyolefin (B) isproduced in a gas phase reactor in the presence of polymer (A). Thereby,it is preferred that the multimodal polymer is at least a bimodalpolymer. More preferably, polymer (A) and polyolefin (B) are bothpolyolefins. The polymer composition of this embodiment comprises 50 to99 wt % of a linear low density polyethylene (LLDPE) having amultimodal, more preferably a bimodal molecular weight distribution(MWD) and more preferably 1 to 50 wt % of a filler (C), preferably aplate- or sheet-like filler such as mica or talc as described above.

In the following, when the description refers to LLDPE, it means that amultimodal, preferably bimodal LLDPE is used, which comprises a lowmolecular weight (LMW) fraction, which is polymer (A) (polyolefin (1)),and a high molecular weight (HMW) fraction, which is polymer (B).

Preferably, the linear low density polyethylene (LLDPE) has a melt indexMFR₂ from 1.0 to 20 g/10 min, more preferably from 2 to 15 g/10 min andmost preferably from 3 to 10 g/10 min. It is preferred that the linearlow density polyethylene (LLDPE) is at below 945 and ranges preferablyfrom 905 to 935 kg/m³, more preferably from 910 to 930 kg/m³, mostpreferably from 915 to 925 kg/m³. If the melt index of the linear lowdensity polyethylene (LLDPE) is lower than 1 g/10 min, a high throughputis not reached. On the other hand, if the melt index MFR₂ is higher than20, the melt strength of the polyethylene suffers.

In addition, it is preferred that the linear low density polyethylene(LLDPE) has a melt flow index MFR₅ from 20 to 40 and preferably a meltflow ratio MFR/MFR₂ from 2.5 to 4.5, more preferably from 2.7 to 4.0.Furthermore, it is preferred that the linear low density polyethylene(LLDPE) has a weight average molecular weight (M_(w)) from 50,000 to150,000 g/mol, more preferably from 60,000 to 100,000 g/mol andpreferably a ratio of the weight average molecular weight to the numberaverage molecular weight M_(w)/M_(n) of 8 to 25, more preferably of 10to 20.

Moreover, the linear low density polyethylene (LLDPE) containscomonomers selected from the group consisting of C₃ alpha-olefin, C₄alpha-olefin, C₅ alpha-olefin, C₆ alpha-olefin, C₇ alpha-olefin, C₈alpha-olefin, C₉ alpha-olefin, C₁₀ alpha-olefin, C₁₁ alpha-olefin, C₁₂alpha-olefin, C₁₃ alpha-olefin, C₁₄ alpha-olefin, C₁₅ alpha-olefin, C₁₆alpha-olefin, C₁₇ alpha-olefin, C₁₈ alpha-olefin, C₁₉ alpha-olefin, C₂₀alpha-olefin. Especially preferred are alpha-olefins selected from thegroup consisting of propylene, 1-butene, 1-pentene, 4-methyl-1-pentene,1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 6-methyl-1-heptene,4-ethyl-1-hexene, 6-ethyl-1-octene and 7-methyl-1-octene. Still morepreferred, alpha-olefins are selected from the group consisting of1-butene, 4-methyl-1-pentene, 1-hexene and 1-octene.

As one requirement of the preferred embodiment is that the polymercomposition is a linear low density polyethylene (LLDPE) the content ofthe comonomer units in the polymer is preferably 0.1 to 1.0 mol %, morepreferably 0.15 to 0.5 mol %.

It is preferred that the linear low density polyethylene (LLDPE) withoutfiller (C) comprises 40 to 60 wt %, more preferably 49 to 55 wt %polymer (A) and 60 to 40 wt %, and more preferably 51 to 45 wt %polyolefin (B).

As stated above, it is preferred that the linear low densitypolyethylene (LLDPE) comprises a LMW fraction, which forms the polymer(A). More preferably, the polymer (A), is a polyolefin (1), mostpreferably an ethylene copolymer containing alpha-olefins other thanethylene and listed above. Furthermore, it is preferred that the polymer(A) of the linear low density polyethylene (LLDPE) has a weight averagemolecular weight (Me) of 10,000 to 60,000 g/mol, more preferably from20,000 to 50,000 g/mol. It is further preferred that polymer (A) of thelinear high density polyethylene (LLDPE), has a density of at least 905to 935 kg/m³, more preferably of at least 910 to 930 kg/m³. In addition,it is preferred that polymer (A) of the linear low density polyethylene(LLDPE) has a melt flow rate MFR₂ from 1.0 to 20.0 g/10 min, morepreferably from 2.0 to 15.0 g/10 min and most preferred from 3 to 10g/10 min.

It is preferred that polyolefin (B) as the linear low densitypolyethylene (LLDPE) is an ethylene copolymer containing one or morealpha-olefins as listed above. Thereby, it is preferred that the amountof comonomer units in polyolefin (B) is from 2.0 to 15.0 mol %, morepreferably from 3.0 to 10.0 mol %. In addition, it is preferred that thepolyolefin (B) in the linear low density polyethylene (LLDPE) has aweight average molecular weight from 80,000 to 300,000 g/mol, morepreferably from 100,000 to 200,000 g/mol.

The filler (C) and other additional components in the linear low densitypolyethylene (LLDPE), are identically used as listed and describedabove. It is in particular preferred that additionally to the LLDPE, awax (2), more preferably a polypropylene wax (2a) or an alkyl-ketenedimer (2b) as defined above is used as an additional polymer (A).

In case two polymers (A) are used, namely polyolefin (1) and wax (2),the amount of wax (2) is 1 to 30 wt %, more preferably 2 to 20 wt % andmost preferably 1 to 10 wt % in the total composition without filler(C). In turn, the composition without filler (C) comprises 70 to 99 wt%, more preferably 80 to 88 wt % and most preferably 90 to 99 wt % LLDPEresulting from polymer (A) and polyolefin (B).

The further preferable embodiment of the present invention is a polymercomposition whereby polymer (A) and polyolefin (B) are preferablymechanically blended. Thereby it is preferred that polymer (A) is a wax(2), more preferably a polypropylene wax (2a) or an alkyl-ketene dimerwax (2b).

In case of polymer (A), where a polypropylene wax (2a) is used, it ispreferred that this wax (2a) has a weight average molecular weight(M_(w)) of 100 to 50,000, more preferably from 100 to 10,000, and mostpreferably from 5,000 to 6,000. In addition, it is preferred that thez-average molecular weight of the polypropylene wax (2a) ranges from 100to 60,000 g/mol, and more preferably from 100 to 10,000 g/mol. It ispreferred that the polypropylene wax (2a) has a number average molecularweight (M_(n)) of 100 to 2,000 g/mol, more preferably 500 to 3,000g/mol. The melting temperature in DSC-analysis of the polypropylene wax(2a) is preferably of 95 to 130° C., more preferably 105 to 115° C.

Preferably, the polypropylene wax (2a) is mechanically blended with anethylene polymer as a polyolefin (B) having an MFR₂ of 6.5 to 8.5 g/10min, more preferably from 7 to 8 g/10 min and a density of 900 to 940kg/m³, more preferably from 915 to 925 kg/m³. It is in particularpreferred that polyolefin (B) is a low density polyethylene (LDPE), or alinear low density polyethylene (LLDPE) as described above.

The mechanically blended polymer including a talc as filler (C) and CaOas a water-absorbent component has preferably a density ranging from1,000 kg/m³ to 1,300 kg/m³, more preferably of 1,150 to 1,200 kg/m³ anda melt flow rate MFR₂ of preferably 8 to 9.5 g/10 min, and morepreferably of 8.5 to 9.0 g/10 min.

The other preferred alternative of a mechanical blend of wax (2) withpolyolefin (B) is to use an alkyl-ketene dimer (2b) as wax (2).Preferably, this alkyl-ketene dimer (2b) has a weight average molecularweight (M_(w)) of 300 to 400 g/mol, more preferably from 320 to 350g/mol. Preferably, the z-average molecular weight of the alkyl-ketenedimer (2b) is from 300 to 400 g/mol, more preferably from 360 to 390g/mol. It is preferred that the alkyl-ketene dimer (2b) has a numberaverage molecular weight (M_(n)) of 200 to 450 g/mol, more preferablyfrom 280 to 300 g/mol. In addition, it is preferred that thealkyl-ketene dimer (2b) has a melting temperature DSC-analysis of 55 to70° C., more preferably from 60 to 65° C.

For polyolefin (B), the same ethylene polymer is used as defined underthe mechanical blend comprising a polypropylene wax (2a).

The density of the mechanically blended polymer composition comprisingan alkyl-ketene dimer (2b) as defined above, an ethylene polymer (B) asdefined above, a filler (C) and a water-absorbent component haspreferably a density of 1,050 to 1,300 kg/m³ and more preferably from1,150 to 1,250 kg/m³. The melt flow rate MFR₂ of this polymercomposition is preferably from 12.5 g/10 min to 14.5 g/10 min and morepreferably from 13 to 14 g/10 min. It is preferred that for thisembodiment for filler (C) talc is employed and for the water absorbentcompound CaO.

Furthermore, the present invention comprises a process for producing themultimodal composition as defined above.

A multimodal or at least bimodal, e.g. bimodal or trimodal, polymer maybe produced by blending two or more monomodal polymers havingdifferently centered maxima in their molecular weight distributions. Theblending may be effected mechanically, e.g. analogously to themechanical blending principles known in the art. Alternatively, themultimodal or at least bimodal, e.g. bimodal or trimodal, polymercomposition may be produced by polymerization using conditions whichcreate a multimodal or at least bimodal, e.g. bimodal or trimodal,polymer composition, i.e. using a catalyst system for mixtures with twoor more different catalytic sides, using two or more stagepolymerization process with different process conditions in thedifferent stages (i.e. different temperatures, pressures, polymerizationmedia, hydrogen partial pressures, etc.). With the polymer as producedin such a sequential step process, i.e. by utilizing reactors coupled inseries, and using different conditions in each reactor, the differentpolymer fractions produced in the different reactors will each havetheir own molecular weight distribution which may differ considerablyfrom one another. The molecular weight distribution curve of theresulting final polymer can be regarded as superimposing of themolecular weight distribution curves of the polymer fractions which willaccordingly show two or more distinct maxima, or at least thedistinctively broadened maxima compared with the curves for individualfractions.

A polymer showing such a molecular weight distribution curve is calledmultimodal, trimodal or bimodal.

Multimodal polymers can be produced according to several processes,which are described, e.g. in WO 92/12182 and WO 97/22633.

A multimodal polymer is preferably produced in a multi-stage process ina multi-stage reaction sequence, such as described in WO 92/12182. Thecontents of this document are included herein by reference.

It is known to produce multimodal or at least bimodal, e.g. bimodal ortrimodal, polymers, preferably multimodal or bimodal olefin-polymers,such as multimodal or bimodal polyethylenes in two or more reactorsconnected in series whereby the compounds (A) and (B) can be produced inany order.

According to the present invention, the main polymerization stages arepreferably carried out as a combination of a slurry gas/gas-phasepolymerization. The slurry polymerization is preferably performed in aso-called loop-reactor.

Optionally, and of more advantage, the main polymerization stages may bepre-ceded by a pre-polymerization in which case up to 20 wt %,preferably 1-10 wt %, more preferably 1-5 wt % of the total amount ofpolymer composition is produced. At the pre-polymerization point, all ofthe catalyst is preferably charged into a loop-reactor and apolymerization is performed as a slurry polymerization. Such apolymerization leads to less fine particles being produced in thefollowing reactors and to a more homogeneous product being obtained inthe end. Such a pre-polymerization is for instance described in WO96/18662.

Generally, the technique results in a multimodal or at least bimodal,e.g. bimodal or trimodal, polymer composition thereby a Ziegler-Natta ormetallocene catalyst in several successive polymerization reactors isused. For example in the production of a bimodal high-densitypolyethylene composition, a first ethylene polymer is produced in thefirst reactor under certain conditions with respect to the hydrogen-gasconcentration, temperature, pressure and so forth. After thepolymerization the reactor-polymer including the catalyst is separatedfrom the reaction mixture and transferred to a second reactor wherefurther polymerization takes place under other conditions.

The components (A) and (B) can be produced with any suitable catalystsystem, preferably a coordination catalyst, such as a Ziegler-Nattacatalyst system, preferably a coordination catalyst, such as aZiegler-Natta catalyst of a transition metal of a group 3-10 of theperiodic table (IUPAC), a metallocene, non-metallocene, in a mannerknown in the art. One example of a preferred Ziegler-Natta catalystcomprises Ti, Mg and Al, such as described in document EP 0 688 794 B1,which is included herewith by reference. It is a high-activitypro-catalyst comprising a particular inorganic support, a curingcompound deposited on the support, wherein the curing compound is thesame as or different from the titanium compound, whereby the inorganicsupport is contacted with an alkyl metal chloride which is soluble in anon-polar hydrocarbon solvent, and has the formula(R_(n)MeCl_(3-n))_(m), wherein R is a C₁ to C₂₀ alkyl group, Me is ametal of Group III(13) of the periodic table, n=1 or 2 and m=1 or 2, togive a first reaction product, and the first reaction product iscontacted with a compound containing hydrocarbyl and hydrocarbyl oxidelinked to magnesium which is soluble in non-polar hydrocarbon solvents,to give a second reaction product, and the second reaction product iscontacted with a titanium compound which contains chlorine, having theformula Cl_(x)Ti(OR^(IV))_(4-x), wherein R^(IV) is a C₂ to C₂₀hydrocarbyl group and x=3 or 4, to give the procatalyst. Preferredsupports are inorganic oxides, more preferably silicon dioxide orsilica. Most preferably silica having an average particle size of 20 μmis used. Even more preferred tri-ethyl aluminium as a cocatalyst isused. Alternatively, a metallocene of group 4 metal can be used.

Preferably, polymer (A), the low molecular weight (LMW) polymer, isproduced with addition or no addition of comonomer in a first reactor,and also the polyolefin (B), the high molecular weight (HMW) polymer, isproduced with addition or no addition, more preferably with addition, ofcomonomer in the second reactor.

The resulting end product consists of an intimate mixture of polymersfrom the two reactors, the different molecular weight distributionoccurs of these polymers together forming a molecular weightdistribution curve having a broad maximum or two maxima, i.e. the endproduct is a multimodal or bimodal polymer mixture. Since multimodaland, in particular, bimodal polymers, preferably ethylene polymers andthe production thereof belong to the prior art, no detailed descriptionis called for here, but reference is made to the above-mentioneddocument WO 92/12182. It will be noted that the order of the reactionstages may be reversed.

Preferably, as stated above, the multimodal polymer compositionaccording to the invention is a bimodal or trimodal polymer composition.It is also preferred that this bimodal or trimodal polymer compositionhas been produced by polymerization as described above under differentpolymerization conditions in two or more polymerization reactorsconnected in series.

Furthermore, it is preferred that for the multimodal compositionaccording to this invention a process is used as defined above whereby

-   a) polymer (A) and polyolefin (B) are produced together in a    multi-stage process comprising a loop reactor and a gas-phase    reactor, wherein polymer (A) is generated in at least one loop    reactor and the polyolefin (B) is generated in a gas-phase reactor    in the presence of the reaction product (A) of the loop reactor, and-   b) filler (C) and the composition comprising polymer (A) and    polyolefin (B) are blended together and compounded.

In particular, a multi-stage process is used as described above.Especially, it is preferred that a loop reactor is operated at 75 to100° C., more preferably in the range of 85 to 100° C. and mostpreferably in the range of 90 to 98° C. Thereby, the pressure ispreferably 58 to 68 bar, more preferably 60 to 65 bar.

Preferably, polymer (A) is prepolymerized in a first loop reactor andthen continuously removed to a second loop reactor where the polymer (A)is further polymerized. It is preferred that the temperature in thesecond loop reactor is 90 to 98° C., more preferably about 95° C.Thereby, the pressure is preferably 58 to 68 bar, more preferably about60 bar.

In addition, it is preferred that in the second loop reactor, theethylene concentration is 4 to 10 mol %, more preferably 5 to 8 mol %and most preferably about 6.7 mol %.

The hydrogen to ethylene mol-ratio highly depends on the catalyst used.It must be adjusted to render the desired melt flow rate MFR of thepolymer withdrawn from the loop reactor. For the preferred catalyst asdescribed it is preferred that the ratio of hydrogen to ethylene is 100to 800 mol/kmol and more preferably 300 to 700 mol/kmol, still morepreferably 400 to 650 mol/kmol and most preferred about 550 mol/kmol.

The polymer slurry is then preferably removed from the loop reactor byusing settling lacks and is then preferably introduced into a flashvessel operating preferably at about 3 bar pressure, where the polymeris separated from most of the fluid phase. The polymer is thenpreferably transferred into a gas-phase reactor operating preferably at75 to 95° C., more preferably 80 to 90° C. and most preferably about 85°C., and at preferably 10 to 50 bar, more preferably 15 to 25 bar andmost preferably about 20 bar.

Additionally, etheylene comonomers were used and hydrogen as well asnitrogen as an inert gas are preferably introduced into the reactor sothat the fractional ethylene in the fluidization gas is preferably 1 to10 mol %, more preferably 1 to 5 mol % and most preferably about 2.5 mol% and the ratio of hydrogen to ethylene is preferably 100 to 400mol/kmol, more preferably 150 to 300 mol/kmol and most preferably about210 mol/kmol.

The comonomer to ethylene ratio has influence on the desired density ofthe bimodal polymer. Hence, it is preferred that the ratio of comonomerto ethylene is 20 to 150 mol/kmol, more preferably 50 to 100 mol/kmoland most preferably about 80 mol/kmol. Preferably, after the polymer iswithdrawn from the gas-phase reactor and then mixed with furtheradditives as anti-oxidants and/or process stabilizers by blending.

The polymer mix of polymer (A) and polyolefin (B) is then blended withfiler (C) and with any suitable method known in the art. These methodsinclude compounding in a twin-screw extruder, like a counter-rotatingtwin-screw extruder or a co-rotating twin-screw extruder and compoundingin a single-screw extruder.

In addition, the present invention comprises a new multi-layer materialcomprising at least

-   a) a substrate as a first layer (I) and-   b) a multimodal polymer composition as described above as at least    one further layer (II).

Preferably, the multi-layer material consists of

-   a) a substrate as a first layer (I) and-   b) a multimodal polymer composition as described above as at least    one further layer (II).

It is further preferred that the multi-layer material is a two-layer orthree-layer material consisting of a substrate as a first layer and of apolymer composition for the second and third layer, whereby preferablyat least the second layer is a polymer composition as defined above. Thelayers can of course be in any order. Optionally, this multi-layermaterial comprises adhesion promoters as tetra-isopropyl titanate,tetra-stearyl titanate, tetrakis(2-ethylhexyl)titanate,poly(dibutyltitanate).

Preferably, the substrate is selected from the group consisting ofpaper, paperboard, aluminium film and plastic film.

Preferably, the multi-layer material comprises as a further layer (III)a low density polyethylene (LDPE). Thereby, it is preferred that the lowdensity polyethylene has a density of 900 to 950 kg/m³, more preferablyfrom 915 to 925 kg/m³. In addition, it is preferred that the melt flowrate MFR₂ of the low density polyethylene (LDPE) is of 2.0 to 20.0 g/10min, more preferably from 3.0 to 10.0 g/10 min.

Preferably, the coating weight of layer (II) comprising the polymercomposition according to the present invention ranges from 5 to 60 g/m²and more preferably from 10 to 45 g/m². Additionally, it is preferredthat the layer (III) comprising a low density polyethylene (LDPE) asdescribed above has a coating weight of 0 to 25, more preferably from 3to 18 g/m².

The present invention also comprises a film, preferably a cast film,comprising the multimodal polymer composition as described above, morepreferably, the film consists of the multimodal polymer composition ofthe present invention.

Furthermore, the present invention provides a process for producing amulti-layer material comprising the inventive polymer composition asdescribed above. Thereby, it is preferred that the multimodal polymercomposition as described above is applied on a substrate by afilm-coating line comprising an unwind, a wind, a chill roll and acoating die. Preferably, the speed of the coating line ranges from 50 to5000 m/min, more preferably from 100 to 1500 m/min. The coating may bedone as any coating line known in the art. It is preferred to employ acoating line with at least two extruders to make it possible to producemultilayered coatings with different polymers. It is also possible tohave arrangements to treat the polymer melt exiting the die to improveadhesion, e.g. by ozone treatment, corona treatment or flame treatment.

In addition, the present invention comprises the use of the multimodalpolymer composition as defined above for extrusion coating, inparticular for extrusion coating producing a multi-layer material asdescribed above.

Furthermore, the present invention relates to the use of the multimodalpolymer composition for films, preferably cast films.

In the following the present invention is demonstrated by means ofexamples.

EXAMPLES Measurements WVTR:

Water vapor transmission rate was measured at 90% relative humidity and38° C. temperature according to the method ASTM E96.

Basis Weight or Coating Weight:

Basis weight (or coating weight) was determined as follows: Five sampleswere cut off from the extrusion coated paper parallel in the transversedirection of the line. The size of the samples was 10 cm×10 cm. Thesamples were dried in an oven at 105° C. for one hour. The samples werethen weighed and the coating weight was calculated as the differencebetween the basis weight of the coated structure and the basis weight ofthe substrate. The result was given as a weight of the plastic persquare meter.

Molecular Weight Averages and Molecular Weight Distribution:

Molecular weight averages and molecular weight distribution weredetermined by ISO 16014, part 2 universal calibration (narrow MWDpolystyrene standards (universal alibration) and a set of 2× mixedbed+1×10⁷ Å Tosohas (JP) columns were used).

Density:

Density was determined according to ISO 1183-1987.

Melt Flow Rate or Melt Index:

Melt flow rate (also referred to as melt index) was determined accordingto ISO 1133, at 190° C. The load used in the measurement is indicated asa subscript, i.e. MFR₂ denotes the MFR measured under 2.16 kg load.

Flow Rate Ratio:

Flow rate ratio is a ratio of two melt flow rates measured for the samepolymer under two different loads. The loads are indicated as asubscript, i.e., FRR_(5/2) denotes the ratio of MFR₅ to MFR₂.

Curling:

Curling was determined by cutting a circular sample having an area of100 cm² within two hours after the coating. The sample is then allowedfreely to curl at the table for two minutes. The curl is then measuredas the difference (in mm) from the table to the curled sheet.

Example 1

A dry blend of pellets was made of 650 kg of the low densitypolyethylene CA8200 of 300 kg of a talc filler Finntalc MO5SL,manufactured and sold by Mondo Minerals and 50 kg of Clariant PP6100 PPwax. This dry blend was then compounded and pelletized by using theabove-mentioned ZSK70 extruder. The melt temperature during theextrusion was 200° C. The composition was then dried at 60° C. for 6hours to remove the moisture. CA8200 is a low density polyethylenedesigned for extrusion coating, produced and marketed by Borealis. It isproduced by free radical polymerization in a high pressure autoclaveprocess. It has an MFR₂ of 7.5 g/10 min and a density of 920 kg/m³.Clariant PP6100 is a low molecular weight propylene polymer having anumber average molecular weight of 2,090 g/mol, weight average molecularweight 5,370 g/mol, z-average molecular weight 10,900 g/mol and meltingtemperature in DSC analysis 109° C. The composition had a density of1,195.7 kg/m³ and MFR₂ of 6.1 g/10 min.

Comparative Example 1

The procedure of Example 1 was repeated, except that the amount ofCA8200 was 700 kg and Clariant PP6100 was not used. Moreover, no dryingat 60° C. was done.

TABLE 1 Data for compositions containing polyolefin and talc used incast films. MFR₂ Density Example Composition g/10 min 920 kg/m³ Example1 LD/PP/talc NA NA Comparative Example 1 LD/—/talc NA NA

Example 2

The composition of Example 1 was used to make a cast film on Collinlaboratory scale cast film line, having a single screw extruder with ascrew diameter of 30 mm and length to diameter (L/D) ratio of 30. Theline speed was about 10 m/s (from 8.9 to 10.3 m/s), the output about 5kg/h (from 4.91 to 6.07 kg/h), the die temperature 250° C. and melttemperature 245° C. The temperature of the chill roll was about 70° C.(68 to 72° C.). The data can be found in Table 2.

The thickness of the film was 45 μm. The WVTR was 5.0 g/m²/24 h.

Example 3

The procedure of Example 2 was repeated, except that the thickness ofthe film was 98 μm. The WVTR was 2.3 g/m²/24 h.

Comparative Example 2

The procedure of Example 3 was repeated, except that the composition ofComparative Example 1 was used in place of the composition of Example 1.Data can be found in Table 2.

TABLE 2 Cast film data. Thickness WVTR Example Composition μ/m g/m²/24 hExample 2 LD/PP/talc 45 5.0 Example 3 LD/PP/talc 98 2.3 ComparativeExample 2 LD/—/talc 102 2.7

1. A multimodal polymer composition comprising at least one polymer (A)having a weight average molecular weight (M_(w)) of less than 60000g/mol; at least one polyolefin (B) having a higher weight averagemolecular weight (M_(w)) than the polymer (A); and a filler wherein thepolymer composition without the filler (C) has a density of 940 kg/m³ orlower.
 2. A polymer composition according to claim 1 wherein the atleast one polymer (A) is (1) a polyolefin (1) having a weight averagemolecular weight (M_(w)) of 10000 to less than 60000 g/mol, or (2) a waxhaving weight average molecular weight (M_(w)) of less than 10000 g/mol.3. A polymer composition according to claim 1 wherein the at least onepolymer (A) is (1) a polyolefin (1) having a weight average molecularweight (M_(w)) of 10000 to less than 60000 g/mol, or (2) a wax havingweight average molecular weight (M_(w)) of less than 10000 g/mol, andwherein the polyolefin (1) is a low density polyethylene (LDPE), alinear low density polyethylene (LLDPE) or a linear medium densitypolyethylene (LMDPE).
 4. A polymer composition according to claim 1wherein the at least one polymer (A) is (1) a polyolefin (1) having aweight average molecular weight (M_(w)) of 10000 to less than 60000g/mol, or (2) a wax (2) having weight average molecular weight (M_(w))of less than 10000 g/mol, and wherein the wax is selected from one ormore of (2a) a polypropylene wax having weight average molecular weight(M_(w)) of less than 10000 g/mol or a polyethylene wax having weightaverage molecular weight (M_(w)) of less than 10000 g/mol, or (2b) analkyl ketene dimer wax having weight average molecular weight (M_(w)) ofless than 10000 g/mol.
 5. A polymer composition according to claim 1wherein the composition comprises (1) a polyolefin (1) having a weightaverage molecular (M_(w)) 10000 to less than 60000 g/mol as a firstpolymer (A) and (2) a wax having weight average molecular weight (M_(w))of less than 10000 g/mol as a second polymer (A).
 6. A polymercomposition according to claim 1 wherein the polymer (A) has a densityof lower than 945 kg/m³.
 7. A polymer composition according to claim 1wherein the multimodal polymer composition is at least a bimodal polymercomposition.
 8. A polymer composition according to claim 1 wherein thepolyolefin (B) has a weight average molecular weight (M_(w)) of higherthan 80000 g/mol.
 9. A polymer composition according to claim 1 whereinthe polyolefin (B) is a polyethylene.
 10. A polymer compositionaccording to claim 1 wherein the polyolefin (B) is a low densitypolyethylene (LDPE), a linear low density polyethylene (LLDPE) or alinear medium density polyethylene (LMDPE).
 11. A polymer compositionaccording to claim 1 wherein the total polymer composition comprises 1to 50 wt % of the polymer (A), 40 to 90 wt % of the polyolefin (B) and 1to 50 wt % of filler (C).
 12. A polymer composition according to claim 1wherein the polymer composition without the filler (C) has melt flowrate MFR₂, according to ISO 1133, at 190° C., of 5 to 20 g/10 min.
 13. Apolymer composition according to claim 1 wherein the polymer compositionwithout the filler (C) has melt flow rate MFR₅, according to ISO 1133,at 190° C., of 20 to 40 g/10 min.
 14. A polymer composition according toclaim 1 wherein the polymer composition without the filler (C) has meltflow ratio MFR₅/MFR₂ of 2.5 to 4.5.
 15. A polymer composition accordingto claim 1 wherein the polymer composition without the filler (C) has aratio of the weight average molecular weight (M_(w)) to the numberaverage molecular weight (M_(n)) of from 8 to
 25. 16. A polymercomposition according to claim 1 wherein 95 wt % of the filler (C) has aparticle size of less than 10 μm.
 17. A polymer composition according toclaim 1 wherein the filler (C) is talc.
 18. A polymer compositionaccording to claim 1 wherein the polymer composition further comprisesantioxidants(s) and/or process stabilizers in an amount of less than2000 ppm in the total composition.
 19. A polymer composition accordingto claim 1 wherein the polymer composition is a linear low densitypolyethylene (LLDPE) or a linear medium density polyethylene (LMDPE),and wherein the polymer (A) and polyolefin (B) are produced in amulti-stage polymerization process.
 20. A polymer composition accordingto claim 1 wherein the polymer composition is a linear low densitypolyethylene (LLDPE) or a linear medium density polyethylene (LMDPE),wherein the polymer (A) and the polyolefin (B) are produced in amulti-stage polymerization process, and wherein the amount of comonomerunits in the linear low density polyethylene (LLDPE) or the linearmedium density polyethylene (LMDPE) is 0.1 to 1.0 mol %.
 21. A polymercomposition according to claim 1 wherein the polymer composition is alinear low density polyethylene (LLDPE) or a linear medium densitypolyethylene (LMDPE), wherein the polymer (A) and the polyolefin (B) areproduced in a multi-stage polymerization process, wherein each of thepolymer (A) and the polyolefin (B) is a linear low density polyethylene(LLDPE) or a linear medium density polyethylene (LMDPE), and wherein thecomonomer units are selected from the group consisting of C₃ α-olefin,C₄ α-olefin, C₅ α-olefin, C₆ α-olefin, C₇ α-olefin, C₈ α-olefin, C₉α-olefin, C₁₀ α-olefin, C₁₁ α-olefin, C₁₂ α-olefin, C₁₃ α-olefin, C₁₄α-olefin, C₁₅ α-olefin, C₁₆ α-olefin, C₁₇ α-olefin, C₁₈ α-olefin, C₁₉α-olefin and C₂₀ α-olefin.
 22. A polymer composition according to claim1 wherein the polymer (A) is a wax selected from one or more of (1) apolypropylene wax having weight average molecular weight (M_(w)) of lessthan 10000 g/mol or (2) a polyethylene wax having weight averagemolecular weight (M_(w)) of less than 10000 g/mol, or (3) an alkylketene dimer wax having weight average molecular weight (M_(w)) of lessthan 10000 g/mol, and wherein the polyolefin (B) is a linear low densitypolyethylene (LLDPE) or low density polyethylene (LDPE).
 23. A polymercomposition according to claim 1 wherein the polymer (A) is a waxselected from one or more of (1) a polypropylene wax having weightaverage molecular weight (M_(w)) of less than 10000 g/mol or (2) apolyethylene wax having weight average molecular weight (M_(w)) of lessthan 10000 g/mol, or (3) a alkyl ketene dimer wax having weight averagemolecular weight (M_(w)) of less than 10000 g/mol, and the polyolefin(B) is a linear low density polyethylene (LLDPE) or low densitypolyethylene (LDPE), and wherein the polymer composition furthercomprises a polyolefin (1) as a second polymer (A), wherein thepolyolefin (1) is a liner low density polyethylene (LLDPE).
 24. Apolymer composition according to claim 1 wherein the polymer compositionis a linear low density polyethylene (LLDPE), wherein polymer(A) andpolyolefin (B) are produced in a multi-staged polymerization process,wherein the amount of comonomer units in a linear low densitypolyethylene (LLDPE) is 0.1 to 1.0 mol %, and the polyolefin (1) ofpolymer A is a linear low density polyethylene (LLDPE) and is the lowermolecular weight fraction of LLDPE, and the polyolefin (B) is a linearlow density polyethylene (LLDPE) and is the higher molecular weightfraction of the LLDPE.
 25. A polymer composition according to claim 1wherein the polymer composition is a linear low density polyethylene(LLDPE), wherein the polymer (A) and the polyolefin (B) are produced ina multi-stage polymerization process, wherein the amount of comonomerunits in a linear low density polyethylene (LLDPE) is 0.1 to 1.0 mol %wherein polyolefin (1) of polymer (A) is a linear low densitypolyethylene (LLDPE) and is the lower molecular weight fraction ofLLDPE, and the polyolefin (B) is a linear low density polyethylene(LLDPE) and is the higher molecular weight fraction of the LLDPE, andwherein the polymer (A) and polyolefin (B) are a mechanical blend.
 26. Amulti-layer material comprising a substrate as a first layer (I) amultimodal polymer composition according to claim 1 as at least a secondlayer (II).
 27. A multi-layer material according to claim 26 wherein thesubstrate is selected from the group consisting of paper, paperboard,aluminium film and plastic film.
 28. A multi-layer material according toclaim 26 wherein the multi-layer material further comprises a thirdlayer (III), which comprises a low density polyethylene (LDPE).
 29. Amulti-layer material according to claim 26 wherein the low densitypolyethylene (LDPE) layer (III) has a melt flow rate MFR₂, according toISO 1133, at 190° C., of at least 5 g/10 min.
 30. A film comprising amultimodal polymer composition according to claim
 1. 31. A process forproducing the composition according to claim 1 comprising the steps of(1) producing the polymer (A) and the polyolefin (B) in a multi-stageprocess comprising a loop reactor and a gas phase reactor, wherein thepolymer (A) is generated in at least one loop reactor and the polyolefin(B) is generated in a gas phase reactor; and (2) blending andcompounding the filler (C) and the composition comprising the polymer(A) and the polyolefin (B).
 32. A process for producing the compositionaccording to claim 31 comprising the steps of (1) producing thecomposition comprising the polymer (A) and the polyolefin (B) using acatalyst, wherein the catalyst is a high activity procatalyst comprisinga particulate inorganic support, and a chlorine compound deposited onthe support, (2) contacting the inorganic support with an alkyl metalchloride which is soluble in non-polar hydrocarbon solvents, and has theformula R_(n)MECL_(3-n))_(m) wherein R is a C₁-C₂₀ alkyl group, Me is ametal of group III(13) of the periodic table, n=1 or 2 and m=1 or 2, togive a first reaction product, (3) contacting the first reaction productwith a compound containing hydrocarbyl and hydrocarbyl oxide linked tomagnesium which is soluble in non-polar hydrocarbon solvents, to give asecond reaction product, and (4) contacting the second reaction productis contacted with a titanium compound which contains chlorine, havingthe formula Cl_(x)Ti(OR^(IV))_(4-x) wherein R^(IV) is a C₂-C₂₀hydrocarbyl group and x is 3 or 4, to give the procatalyst, and whereinthe titanium compound which contains chlorine may be the same ordifferent than the chlorine compound used in step
 1. 33. A process forproducing a multi-layer material according to claim 26 wherein themultimodal polymer composition comprises at least one polymer (A) havinga weight average molecular weight (M_(w)) of less than 6000 g/mol; atleast one polyolefin (B) having a higher weight average molecular weight(M_(w)) than polymer (A); and a filler (C), and wherein the polymercomposition without (C) has a density of 940 kg/m³ or lower is appliedon the substrate by a film coating line comprising an unwind, a wind, achill roll and a coating die.
 34. A method for extrusion coatingcomprising applying to a material to be coated the multimodal polymercomposition according to claim
 1. 35. The method according to claim 34wherein the the material to be coated is a multi-layer materialcomprising a substrate as a first layer (I) the multimodal polymercomposition as at least a second layer (II).
 36. A method comprisingpreparing a film from the multimodal polymer composition according toclaim
 1. 37. The method of claim 25, wherein the mechanical blend is anin-situ blend produced in a multi-stage polymerization process.
 38. Themethod of claim 36, wherein the film is a cast film.
 39. A polymercomposition according to claim 1 wherein the composition comprises apolyolefin (1) having a weight average molecular weight (M_(w)) of 10000to less than 60000 g/mol as the polymer (A) and a wax (2) having weightaverage molecular weight (M_(w)) of less than 10000 g/mol as a secondpolymer (A), wherein the polyolefin (1) is a low density polyethylene(LDPE), a linear low density polyethylene (LLDPE), or a linear mediumdensity polyethylene (LMDPE).
 40. A polymer composition according toclaim 1 wherein the composition comprises a polyolefin (1) having aweight average molecular weight (M_(w)) of 10000 to less than 60000g/mol as the polymer (A) and a wax (2) having weight average molecularweight (M_(w)) of less than 10000 g/mol as a second polymer (A), whereinthe wax (2) is selected from one or more of (2a) a polypropylene waxhaving weight average molecular weight (M_(w)) of less than 10000 g/molor a polyethylene wax having weight average molecular weight (M_(w)) ofless than 10000 g/mol, or (2b) an alkyl ketene dimer wax having weightaverage molecular weight (M_(w)) of less than 10000 g/mol.
 41. A polymercomposition according to claim 1 wherein the polymer composition is alinear low density polyethylene (LLDPE) wherein the polymer (A) and thepolyolefin (B) are produced in a multi-stage polymerization process, thecomonomer units are selected from the group consisting of C₃ α-olefin,C₄ α-olefin, C₅ α-olefin, C₆ α-olefin, C₇ α-olefin, C₈ α-olefin, C₉α-olefin, C₁₀ α-olefin, C₁₁ α-olefin, C₁₂ α-olefin, C₁₃ α-olefin, C₁₄α-olefin, C₁₅ α-olefin, C₁₆ α-olefin, C₁₇ α-olefin, C₁₈ α-olefin, C₁₉α-olefin and C₂₀ α-olefin, and the polyolefin (1) of the polymer (A) isa linear low density polyethylene (LLDPE) and is the lower molecularweight fraction of LLDPE, and the polyolefin (B) is a linear low densitypolyethylene (LLDPE) and is the higher molecular weight fraction of theLLDPE.
 42. A polymer composition according to claim 1 wherein thepolymer composition is a linear low density polyethylene (LLDPE),wherein the polymer (A) and the polyolefin (B) are produced in amulti-stage polymerization process, the comonomer units are selectedfrom the group consisting of C₃ α-olefin, C₄ α-olefin, C₅ α-olefin, C₆α-olefin, C₇ α-olefin, C₈ α-olefin, C₉ α-olefin, C₁₀ α-olefin, C₁₁α-olefin, C₁₂ α-olefin, C₁₃ α-olefin, C₁₄ α-olefin, C₁₅ α-olefin, C₁₆α-olefin, C₁₇ α-olefin, C₁₈ α-olefin, C₁₉ α-olefin and C₂₀ α-olefin, andthe polyolefin (1) of the polymer (A) is a linear low densitypolyethylene (LLDPE) and is the lower molecular weight fraction ofLLDPE, and the polyolefin (B) is a linear low density polyethylene(LLDPE) and is the higher molecular weight fraction of the LLDPE, andwherein the polymer (A) and the polyolefin (B) are a mechanical blend.43. The polymer composition of claim 42, wherein the mechanical blend isan in-situ blend produced in a multi-stage polymerization process.